Coherent plasmons inn-doped GaAs

Femtosecond laser excitation of bulk $n$-doped GaAs leads to coherent plasmon excitations that emit intense submillimeter wave radiation. We investigated the underlying plasmon dynamics in time-resolved experiments on the emitted THz radiation. The results show that THz pulses are emitted due to the coherent oscillation of the extrinsic electron plasma in the bulk. The plasmon excitations are started by single-sided screening of the surface depletion field after photoexcitation. Temperature-dependent measurements indicate that the plasmon damping is due to phonon scattering.